C++ GlobalValue::eraseFromParent方法代码示例

void ModuleLinker::dropReplacedComdat(
    GlobalValue &GV, const DenseSet<const Comdat *> &ReplacedDstComdats) {
  Comdat *C = GV.getComdat();
  if (!C)
    return;
  if (!ReplacedDstComdats.count(C))
    return;
  if (GV.use_empty()) {
    GV.eraseFromParent();
    return;
  }

  if (auto *F = dyn_cast<Function>(&GV)) {
    F->deleteBody();
  } else if (auto *Var = dyn_cast<GlobalVariable>(&GV)) {
    Var->setInitializer(nullptr);
  } else {
    auto &Alias = cast<GlobalAlias>(GV);
    Module &M = *Alias.getParent();
    PointerType &Ty = *cast<PointerType>(Alias.getType());
    GlobalValue *Declaration;
    if (auto *FTy = dyn_cast<FunctionType>(Alias.getValueType())) {
      Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage, "", &M);
    } else {
      Declaration =
          new GlobalVariable(M, Ty.getElementType(), /*isConstant*/ false,
                             GlobalValue::ExternalLinkage,
                             /*Initializer*/ nullptr);
    }
    Declaration->takeName(&Alias);
    Alias.replaceAllUsesWith(Declaration);
    Alias.eraseFromParent();
  }
}

/// linkFunctionProto - Link the function in the source module into the
/// destination module if needed, setting up mapping information.
bool ModuleLinker::linkFunctionProto(Function *SF) {
  GlobalValue *DGV = getLinkedToGlobal(SF);
  llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;

  if (DGV) {
    GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
    bool LinkFromSrc = false;
    GlobalValue::VisibilityTypes NV;
    if (getLinkageResult(DGV, SF, NewLinkage, NV, LinkFromSrc))
      return true;
    NewVisibility = NV;

    if (!LinkFromSrc) {
      // Set calculated linkage
      DGV->setLinkage(NewLinkage);
      DGV->setVisibility(*NewVisibility);

      // Make sure to remember this mapping.
      ValueMap[SF] = ConstantExpr::getBitCast(DGV, TypeMap.get(SF->getType()));
      
      // Track the function from the source module so we don't attempt to remap 
      // it.
      DoNotLinkFromSource.insert(SF);
      
      return false;
    }
  }
  
  // If there is no linkage to be performed or we are linking from the source,
  // bring SF over.
  Function *NewDF = Function::Create(TypeMap.get(SF->getFunctionType()),
                                     SF->getLinkage(), SF->getName(), DstM);
  CopyGVAttributes(NewDF, SF);
  if (NewVisibility)
    NewDF->setVisibility(*NewVisibility);

  if (DGV) {
    // Any uses of DF need to change to NewDF, with cast.
    DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDF, DGV->getType()));
    DGV->eraseFromParent();
  } else {
    // Internal, LO_ODR, or LO linkage - stick in set to ignore and lazily link.
    if (SF->hasLocalLinkage() || SF->hasLinkOnceLinkage() ||
        SF->hasAvailableExternallyLinkage()) {
      DoNotLinkFromSource.insert(SF);
      LazilyLinkFunctions.push_back(SF);
    }
  }
  
  ValueMap[SF] = NewDF;
  return false;
}

/// LinkAliasProto - Set up prototypes for any aliases that come over from the
/// source module.
bool ModuleLinker::linkAliasProto(GlobalAlias *SGA) {
  GlobalValue *DGV = getLinkedToGlobal(SGA);
  llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;

  if (DGV) {
    GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
    GlobalValue::VisibilityTypes NV;
    bool LinkFromSrc = false;
    if (getLinkageResult(DGV, SGA, NewLinkage, NV, LinkFromSrc))
      return true;
    NewVisibility = NV;

    if (!LinkFromSrc) {
      // Set calculated linkage.
      DGV->setLinkage(NewLinkage);
      DGV->setVisibility(*NewVisibility);

      // Make sure to remember this mapping.
      ValueMap[SGA] = ConstantExpr::getBitCast(DGV,TypeMap.get(SGA->getType()));
      
      // Track the alias from the source module so we don't attempt to remap it.
      DoNotLinkFromSource.insert(SGA);
      
      return false;
    }
  }
  
  // If there is no linkage to be performed or we're linking from the source,
  // bring over SGA.
  GlobalAlias *NewDA = new GlobalAlias(TypeMap.get(SGA->getType()),
                                       SGA->getLinkage(), SGA->getName(),
                                       /*aliasee*/0, DstM);
  CopyGVAttributes(NewDA, SGA);
  if (NewVisibility)
    NewDA->setVisibility(*NewVisibility);

  if (DGV) {
    // Any uses of DGV need to change to NewDA, with cast.
    DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDA, DGV->getType()));
    DGV->eraseFromParent();
  }
  
  ValueMap[SGA] = NewDA;
  return false;
}

// destructively move the contents of src into dest
// this assumes that the targets of the two modules are the same
// including the DataLayout and ModuleFlags (for example)
// and that there is no module-level assembly
static void jl_merge_module(Module *dest, std::unique_ptr<Module> src)
{
    assert(dest != src.get());
    for (Module::global_iterator I = src->global_begin(), E = src->global_end(); I != E;) {
        GlobalVariable *sG = &*I;
        GlobalValue *dG = dest->getNamedValue(sG->getName());
        ++I;
        // Replace a declaration with the definition:
        if (dG) {
            if (sG->isDeclaration()) {
                sG->replaceAllUsesWith(dG);
                sG->eraseFromParent();
                continue;
            }
            else {
                dG->replaceAllUsesWith(sG);
                dG->eraseFromParent();
            }
        }
        // Reparent the global variable:
        sG->removeFromParent();
        dest->getGlobalList().push_back(sG);
        // Comdat is owned by the Module, recreate it in the new parent:
        addComdat(sG);
    }

    for (Module::iterator I = src->begin(), E = src->end(); I != E;) {
        Function *sG = &*I;
        GlobalValue *dG = dest->getNamedValue(sG->getName());
        ++I;
        // Replace a declaration with the definition:
        if (dG) {
            if (sG->isDeclaration()) {
                sG->replaceAllUsesWith(dG);
                sG->eraseFromParent();
                continue;
            }
            else {
                dG->replaceAllUsesWith(sG);
                dG->eraseFromParent();
            }
        }
        // Reparent the global variable:
        sG->removeFromParent();
        dest->getFunctionList().push_back(sG);
        // Comdat is owned by the Module, recreate it in the new parent:
        addComdat(sG);
    }

    for (Module::alias_iterator I = src->alias_begin(), E = src->alias_end(); I != E;) {
        GlobalAlias *sG = &*I;
        GlobalValue *dG = dest->getNamedValue(sG->getName());
        ++I;
        if (dG) {
            if (!dG->isDeclaration()) { // aliases are always definitions, so this test is reversed from the above two
                sG->replaceAllUsesWith(dG);
                sG->eraseFromParent();
                continue;
            }
            else {
                dG->replaceAllUsesWith(sG);
                dG->eraseFromParent();
            }
        }
        sG->removeFromParent();
        dest->getAliasList().push_back(sG);
    }

    // metadata nodes need to be explicitly merged not just copied
    // so there are special passes here for each known type of metadata
    NamedMDNode *sNMD = src->getNamedMetadata("llvm.dbg.cu");
    if (sNMD) {
        NamedMDNode *dNMD = dest->getOrInsertNamedMetadata("llvm.dbg.cu");
#ifdef LLVM35
        for (NamedMDNode::op_iterator I = sNMD->op_begin(), E = sNMD->op_end(); I != E; ++I) {
            dNMD->addOperand(*I);
        }
#else
        for (unsigned i = 0, l = sNMD->getNumOperands(); i < l; i++) {
            dNMD->addOperand(sNMD->getOperand(i));
        }
#endif
    }
}

Expected<Constant *> IRLinker::linkGlobalValueProto(GlobalValue *SGV,
                                                    bool ForAlias) {
  GlobalValue *DGV = getLinkedToGlobal(SGV);

  bool ShouldLink = shouldLink(DGV, *SGV);

  // just missing from map
  if (ShouldLink) {
    auto I = ValueMap.find(SGV);
    if (I != ValueMap.end())
      return cast<Constant>(I->second);

    I = AliasValueMap.find(SGV);
    if (I != AliasValueMap.end())
      return cast<Constant>(I->second);
  }

  if (!ShouldLink && ForAlias)
    DGV = nullptr;

  // Handle the ultra special appending linkage case first.
  assert(!DGV || SGV->hasAppendingLinkage() == DGV->hasAppendingLinkage());
  if (SGV->hasAppendingLinkage())
    return linkAppendingVarProto(cast_or_null<GlobalVariable>(DGV),
                                 cast<GlobalVariable>(SGV));

  GlobalValue *NewGV;
  if (DGV && !ShouldLink) {
    NewGV = DGV;
  } else {
    // If we are done linking global value bodies (i.e. we are performing
    // metadata linking), don't link in the global value due to this
    // reference, simply map it to null.
    if (DoneLinkingBodies)
      return nullptr;

    NewGV = copyGlobalValueProto(SGV, ShouldLink);
    if (ShouldLink || !ForAlias)
      forceRenaming(NewGV, SGV->getName());
  }

  // Overloaded intrinsics have overloaded types names as part of their
  // names. If we renamed overloaded types we should rename the intrinsic
  // as well.
  if (Function *F = dyn_cast<Function>(NewGV))
    if (auto Remangled = Intrinsic::remangleIntrinsicFunction(F))
      NewGV = Remangled.getValue();

  if (ShouldLink || ForAlias) {
    if (const Comdat *SC = SGV->getComdat()) {
      if (auto *GO = dyn_cast<GlobalObject>(NewGV)) {
        Comdat *DC = DstM.getOrInsertComdat(SC->getName());
        DC->setSelectionKind(SC->getSelectionKind());
        GO->setComdat(DC);
      }
    }
  }

  if (!ShouldLink && ForAlias)
    NewGV->setLinkage(GlobalValue::InternalLinkage);

  Constant *C = NewGV;
  if (DGV)
    C = ConstantExpr::getBitCast(NewGV, TypeMap.get(SGV->getType()));

  if (DGV && NewGV != DGV) {
    DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewGV, DGV->getType()));
    DGV->eraseFromParent();
  }

  return C;
}

/// linkGlobalProto - Loop through the global variables in the src module and
/// merge them into the dest module.
bool ModuleLinker::linkGlobalProto(GlobalVariable *SGV) {
  GlobalValue *DGV = getLinkedToGlobal(SGV);
  llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;

  if (DGV) {
    // Concatenation of appending linkage variables is magic and handled later.
    if (DGV->hasAppendingLinkage() || SGV->hasAppendingLinkage())
      return linkAppendingVarProto(cast<GlobalVariable>(DGV), SGV);
    
    // Determine whether linkage of these two globals follows the source
    // module's definition or the destination module's definition.
    GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
    GlobalValue::VisibilityTypes NV;
    bool LinkFromSrc = false;
    if (getLinkageResult(DGV, SGV, NewLinkage, NV, LinkFromSrc))
      return true;
    NewVisibility = NV;

    // If we're not linking from the source, then keep the definition that we
    // have.
    if (!LinkFromSrc) {
      // Special case for const propagation.
      if (GlobalVariable *DGVar = dyn_cast<GlobalVariable>(DGV))
        if (DGVar->isDeclaration() && SGV->isConstant() && !DGVar->isConstant())
          DGVar->setConstant(true);
      
      // Set calculated linkage and visibility.
      DGV->setLinkage(NewLinkage);
      DGV->setVisibility(*NewVisibility);

      // Make sure to remember this mapping.
      ValueMap[SGV] = ConstantExpr::getBitCast(DGV,TypeMap.get(SGV->getType()));
      
      // Track the source global so that we don't attempt to copy it over when 
      // processing global initializers.
      DoNotLinkFromSource.insert(SGV);
      
      return false;
    }
  }
  
  // No linking to be performed or linking from the source: simply create an
  // identical version of the symbol over in the dest module... the
  // initializer will be filled in later by LinkGlobalInits.
  GlobalVariable *NewDGV =
    new GlobalVariable(*DstM, TypeMap.get(SGV->getType()->getElementType()),
                       SGV->isConstant(), SGV->getLinkage(), /*init*/0,
                       SGV->getName(), /*insertbefore*/0,
                       SGV->isThreadLocal(),
                       SGV->getType()->getAddressSpace());
  // Propagate alignment, visibility and section info.
  CopyGVAttributes(NewDGV, SGV);
  if (NewVisibility)
    NewDGV->setVisibility(*NewVisibility);

  if (DGV) {
    DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDGV, DGV->getType()));
    DGV->eraseFromParent();
  }
  
  // Make sure to remember this mapping.
  ValueMap[SGV] = NewDGV;
  return false;
}